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Re: LED below 10mA and 1.4V

Look at the 3mm and 5mm LEDs from different companies as anything high powered isn't even close to that drive current. As idleprocess said...your probably not going to find green and blue LEDs in that voltage range. You'd probably be hard pressed to find red in that range too. What is you application as it may help to know how you are going to use these?

Re: LED below 10mA and 1.4V

Originally Posted by Optical Inferno

Look at the 3mm and 5mm LEDs from different companies as anything high powered isn't even close to that drive current. As idleprocess said...your probably not going to find green and blue LEDs in that voltage range. You'd probably be hard pressed to find red in that range too. What is you application as it may help to know how you are going to use these?

Yes, about my application, it is good to mention that i need the LED to be spotted from dozens of meters away, let's say 50 meter +-
I don't mind that there will be 3 LEDs in my housing, one for each color.
This is for indoor use where the light intensity is about 400 LUX.
About the voltage, this is my power source (1.4V) but i can amplify it i guess...
Is that possible?

Re: LED below 10mA and 1.4V

Originally Posted by mrgoos

Yes, about my application, it is good to mention that i need the LED to be spotted from dozens of meters away, let's say 50 meter +-
I don't mind that there will be 3 LEDs in my housing, one for each color.
This is for indoor use where the light intensity is about 400 LUX.
About the voltage, this is my power source (1.4V) but i can amplify it i guess...
Is that possible?

Thanks a lot for your replies.

You will need a boost circuit and then should be able to use the LED(s) of choice.

Re: LED below 10mA and 1.4V

You will need a boost circuit and then should be able to use the LED(s) of choice.

I designed and have available for sale a low power LED boost circuit board that runs well from 1.5 volts up to the LED's vf (runs to about 0.8 volts on the low end).

If the LED's end up needing different drive levels due to their different vf, you could of course have a single boost circuit per LED, each boost circuit with the corresponding inductor to get the right amount of current to that particular LED.

I can vary the current level depending on the inductor chosen. For example, with the default 4.7uH inductor I get 50-60mA to the LED with an input voltage of 1.5volts. With something like a 47uH inductor I was measuring about 8-10mA at 1.5 volts, so these might work well for you.

Re: LED below 10mA and 1.4V

You're running into physical boundaries here, the operating voltage of the die is at least equal to the energy required to produce the desired wavelength. Wiki says "E=hf" and "c=λf". Roughly : energy is equal to frequency times a certain constant (Planck's). Likewise, propagation velocity of the wave is equal to the wavelength times the frequency. Since we know the velocity (light speed), we can rearrange that a bit, telling us that "E= hc/λ" or "λ=hc/E". Working out this, remembering that voltage difference represents a certain energy, it roughly means that λ=1240/voltage. If you thus want green light (545 nanometer), you'll need at least 2.3V. For gallium nitride (the used stuff for most LEDs) the bandgap (creating the photons out of that voltage difference) is somewhere at 3.4V, producing a violet or near-UV light, which is then reformed to other colours which together produces 'white' light.
In most cases you can simply use a booster circuit like the one wquiles posted, or anything else that keeps the voltage at the required minimum, independant of what voltage you supply.

tl;dr: forget anything lower than 3V for white or blue LEDs. Use a booster circuit if you can't provide that.

Re: LED below 10mA and 1.4V

First of all, thank you all for your answers.
The problem of using the boost circuit is that there's nothing to do with the fact that P=VI.
If the power (supposed to) stay the same, the current will drop. The power output that I'm using has 325mW.
Currently I'm checking POC of a solar power source that has a 0.5v and 650uA (this is why 325mW). the 650 part is impressive but once i will boost the voltage, the current will drop so it might be a bit more efficient than other solar power sources that i have tested but i will need lots of those in order to make the LED light to dozens of meters.

Re: LED below 10mA and 1.4V

Originally Posted by mrgoos

First of all, thank you all for your answers.
The problem of using the boost circuit is that there's nothing to do with the fact that P=VI.
If the power (supposed to) stay the same, the current will drop. The power output that I'm using has 325mW.
Currently I'm checking POC of a solar power source that has a 0.5v and 650uA (this is why 325mW). the 650 part is impressive but once i will boost the voltage, the current will drop so it might be a bit more efficient than other solar power sources that i have tested but i will need lots of those in order to make the LED light to dozens of meters.

Please correct me if I'm wrong.
Thank you all.

If you are using solar cells it is probably better to keep adding them in series to get the voltage high enough to sustain the power level required.

Re: LED below 10mA and 1.4V

Sure, i can add them serially to get the voltage higher but the current will remain the same.
Let's say i want to get 3v. I will add serially 6 pieces (they are small, it's OK). now i have 3v with current of 650uA. What bright LED will be shown for dozens of meters with those properties?

Re: LED below 10mA and 1.4V

Originally Posted by mrgoos

Sure, i can add them serially to get the voltage higher but the current will remain the same.
Let's say i want to get 3v. I will add serially 6 pieces (they are small, it's OK). now i have 3v with current of 650uA. What bright LED will be shown for dozens of meters with those properties?

Thanks.

650uA is 2/3 of a milliamp, if dozens of meters means perhaps 100 feet or more then I would say you probably need a drive current at least 5ma to whatever LED(s) you use and have a focused LED instead of a wide angle one. You could use 7 cells in series for 3.5v and take arrays of such in parallel to increase current output. 9 x 7series would equal about 6ma at 3.5v which should be noticeable 100 feet away if pointed in the right direction.

Re: LED below 10mA and 1.4V

Well, i need to make sure that i have enough power for the LED.
From my calculations if i add 9 units i will have 2.34mW power. Is that enough for my demands?
I need red, green and blue LED to be spotted from 100 feet as you wrote +- and with an angle, in order to be spotted from any direction.
Is that even possible? Do i need to add something to the circuit?
BTW the subject of the thread is false. i don't have 1.4v, only 0.5v and 650uA as i wrote previously.

Re: LED below 10mA and 1.4V

if you want red green and blue constantly, then no 780 uW of power each wont be enough. monochromatic 555nm green light has 683 lumens per watt, (since the eye is most sensitive to it), means that the green LED would emit half a lumen (with an idea 100% efficiency of electricity to light not likely) comes in at 0.00008842 lux at 30 meters and a 180 degree viewing angle per http://ledstuff.co.nz/data_calculato...ocmopzepnozrsa well under what you could see.

Youre going to need a circuit that blinks the LEDs in order to have hopes of anything noticeable

Re: LED below 10mA and 1.4V

Looking at the power your panel supplies I really wonder what size they are. Most panels can get you around 100 W / m^2 (in direct sunlight... any cloud makes numbers drop like a rock), so you get roughly 10 mW per square centimeter. That probably is enough to drive a power LED, albeit at a very low power, so it won't be visible from a distance unless it's completely dark. Still, if I look at the thread here about XM-L at low power you should get several lumens from it.

Re: LED below 10mA and 1.4V

Originally Posted by mrgoos

BTW the subject of the thread is false. i don't have 1.4v, only 0.5v and 650uA as i wrote previously.

500 millivolts and 650 microamps means you have 325 microwatts to work with. I don't think that's enough power to do anything useful with unless you store the collected power in a super/ultracapacitor and only need the light to operate for seconds once a day or so. I'm not sure that there are any conventional circuits that will work with such low voltage, nevermind the current. You appear to need a great deal more power to achieve your goal - nearly 1000 times as much as you have available.

You're dealing with such uselessly minute amounts of power and being exceptionally cryptic about your baffling constraints. If it's a one-off exercise, you're probably going to expend orders of magnitude more effort and cost trying to make it work than simply adding more power will get you. If it's something being produced in some quantity, get an engineer to help but be prepared to accept that this may not be achievable.

Last edited by idleprocess; 04-21-2012 at 09:45 AM.

I apologize that this letter is so long; I did not have time to write a short letter

Re: LED below 10mA and 1.4V

Originally Posted by Freeze_XJ

Looking at the power your panel supplies I really wonder what size they are. Most panels can get you around 100 W / m^2 (in direct sunlight... any cloud makes numbers drop like a rock), so you get roughly 10 mW per square centimeter. That probably is enough to drive a power LED, albeit at a very low power, so it won't be visible from a distance unless it's completely dark. Still, if I look at the thread here about XM-L at low power you should get several lumens from it.

I'm using solar panel for indoors... This is why i have these properties.
And it's a very efficient one.

Yes, i have 325mW and i can add some together but i see that it won't help a lot.
I could add 10 or so...

Re: LED below 10mA and 1.4V

Blinking reduces power requirements by 50%, but does require you to wire a circuit to it. Those tend to be quite efficient for higher powers, but at these levels (assuming you have to build one in a shed from COTS caps and ICs) the power to keep them active is going to eclipse any gains you might possibly get. Your problem is that you really can't use anything more than the very basic electronics (a few resistors and a cap, perhaps a coil) or you'll loose too much power there. Also know that most common ICs tend to run on >3V, too.

(note that this assumes microwatts, if you really have the milliwatts your margin increases by quite a lot. In that case a strobe could be an option, ie 5-10% of the time 'on', otherwise 'off', so you get 10-20 times the brightness you'd otherwise have, as well as attract attention :P)

Re: LED below 10mA and 1.4V

Originally Posted by idleprocess

500 millivolts and 650 microamps means you have 325 microwatts

BTW that's not true.
If i had 0.5v and 650uA i will have power of 0.325mW and not 325mW.
So i do have a current of 650uA and voltage of 0.4v so the power for 1 unit that i have is 260uW.
I understand that it's not much and even if i add 10 units i will get 2.6mW which apparently won't be enough for LED right?
2.6mW could give me 1mA and 2.6V - Is there a LED that will work under these conditions?
What is the minimum that i should get in order to meet my requirements?

Re: LED below 10mA and 1.4V

Originally Posted by mrgoos

BTW that's not true.
If i had 0.5v and 650uA i will have power of 0.325mW and not 325mW.

0.5V * 0.00065A = 0.000325W ... 325 microwatts (10^-6 watts) if you stick to common engineering notation (keeping your multiplier >1) or 0.325 milliwatts (10^-3 watts) if you really want to stick to milli- notation - which is a bit confusing and misleading, thus the preference to use multipliers >1.

So i do have a current of 650uA and voltage of 0.4v so the power for 1 unit that i have is 260uW.
I understand that it's not much and even if i add 10 units i will get 2.6mW which apparently won't be enough for LED right?
2.6mW could give me 1mA and 2.6V - Is there a LED that will work under these conditions?
What is the minimum that i should get in order to meet my requirements?

Thanks.

You will have to await a response from someone that can design these circuits; I'm good with basic Ohm's law stuff, LED basics, and little else.

You'll need to produce close to 3.6V and at least a few milliamps to run blue/green LED's. With some sort of power storage, DC/DC conversion, and intermittent use you could do that with 2.6mW. If your usage is truly intermittent and your storage capacity can easily meet what your solar panels generate, you could likely run them at full brightness for several seconds an hour.

I apologize that this letter is so long; I did not have time to write a short letter

Re: LED below 10mA and 1.4V

Originally Posted by Freeze_XJ

Blinking reduces power requirements by 50%, but does require you to wire a circuit to it. Those tend to be quite efficient for higher powers, but at these levels (assuming you have to build one in a shed from COTS caps and ICs) the power to keep them active is going to eclipse any gains you might possibly get. Your problem is that you really can't use anything more than the very basic electronics (a few resistors and a cap, perhaps a coil) or you'll loose too much power there. Also know that most common ICs tend to run on >3V, too.

(note that this assumes microwatts, if you really have the milliwatts your margin increases by quite a lot. In that case a strobe could be an option, ie 5-10% of the time 'on', otherwise 'off', so you get 10-20 times the brightness you'd otherwise have, as well as attract attention :P)

When youre at ultra low power requirements like this, you dont use normal ICs so much as discreets in cleverly designed circuits. I'd look at BEAM robotics stuff for inspiration.